Systems, articles, and methods for electromyography sensors

ABSTRACT

Systems, articles, and methods for surface electromyography (“EMG”) sensors that combine elements from traditional capacitive and resistive EMG sensors are described. For example, capacitive EMG sensors that are adapted to resistively couple to a user&#39;s skin are described. Resistive coupling between a sensor electrode and the user&#39;s skin is galvanically isolated from the sensor circuitry by a discrete component capacitor included downstream from the sensor electrode. The combination of a resistively coupled electrode and a discrete component capacitor provides the respective benefits of traditional resistive and capacitive (respectively) EMG sensor designs while mitigating respective drawbacks of each approach. A wearable EMG device that provides a component of a human-electronics interface and incorporates such capacitive EMG sensors is also described.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 16/292,609, filed Mar. 5, 2019, which is a continuation of U.S. application Ser. No. 15/799,628, filed Oct. 31, 2017, now U.S. Pat. No. 10,251,577, which is a division of U.S. application Ser. No. 14/553,657, filed Nov. 25, 2014, now U.S. Pat. No. 10,188,309, which claims the benefit of U.S. Provisional Application No. 61/909,786, filed Nov. 27, 2013, the disclosures of each of which are incorporated, in their entirety, by this reference.

BACKGROUND Technical Field

The present systems, articles, and methods generally relate to electromyography and particularly relate to capacitive electromyography sensors that resistively couple to the user's body.

Description of the Related Art

Wearable Electronic Devices

Electronic devices are commonplace throughout most of the world today. Advancements in integrated circuit technology have enabled the development of electronic devices that are sufficiently small and lightweight to be carried by the user. Such “portable” electronic devices may include on-board power supplies (such as batteries or other power storage systems) and may be designed to operate without any wire-connections to other electronic systems; however, a small and lightweight electronic device may still be considered portable even if it includes a wire-connection to another electronic system. For example, a microphone may be considered a portable electronic device whether it is operated wirelessly or through a wire-connection.

The convenience afforded by the portability of electronic devices has fostered a huge industry. Smartphones, audio players, laptop computers, tablet computers, and ebook readers are all examples of portable electronic devices. However, the convenience of being able to carry a portable electronic device has also introduced the inconvenience of having one's hand(s) encumbered by the device itself. This problem is addressed by making an electronic device not only portable, but wearable.

A wearable electronic device is any portable electronic device that a user can carry without physically grasping, clutching, or otherwise holding onto the device with their hands. For example, a wearable electronic device may be attached or coupled to the user by a strap or straps, a band or bands, a clip or clips, an adhesive, a pin and clasp, an article of clothing, tension or elastic support, an interference fit, an ergonomic form, etc. Examples of wearable electronic devices include digital wristwatches, electronic armbands, electronic rings, electronic ankle-bracelets or “anklets,” head-mounted electronic display units, hearing aids, and so on.

Human-Electronics Interfaces

A wearable electronic device may provide direct functionality for a user (such as audio playback, data display, computing functions, etc.) or it may provide electronics to interact with, communicate with, or control another electronic device. For example, a wearable electronic device may include sensors that are responsive to (i.e., detect and provide one or more signal(s) in response to detecting) inputs effected by a user and transmit signals to another electronic device based on those inputs. Sensor-types and input-types may each take on a variety of forms, including but not limited to: tactile sensors (e.g., buttons, switches, touchpads, or keys) providing manual control, acoustic sensors providing voice-control, electromyography sensors providing gesture control, or accelerometers providing gesture control.

A human-computer interface (“HCl”) is an example of a human-electronics interface. The present systems, articles, and methods may be applied to HCIs, but may also be applied to any other form of human-electronics interface.

Electromyography Sensors

Electromyography (“EMG”) is a process for detecting and processing the electrical signals generated by muscle activity. EMG devices employ EMG sensors that are responsive to the range of electrical potentials (typically μV-mV) involved in muscle activity. EMG signals may be used in a wide variety of applications, including: medical monitoring and diagnosis, muscle rehabilitation, exercise and training, prosthetic control, and even in controlling functions of electronic devices (i.e., in human-electronics interfaces).

There are two main types of EMG sensors: intramuscular EMG sensors and surface EMG sensors. As the names suggest, intramuscular EMG sensors are designed to penetrate the skin and measure EMG signals from within the muscle tissue, while surface EMG sensors are designed to rest on an exposed surface of the skin and measure EMG signals from there. Intramuscular EMG sensor measurements can be much more precise than surface EMG sensor measurements; however, intramuscular EMG sensors must be applied by a trained professional, are obviously more invasive, and are less desirable from the patient's point of view. The use of intramuscular EMG sensors is generally limited to clinical settings.

Surface EMG sensors can be applied with ease, are much more comfortable for the patient/user, and are therefore more appropriate for non-clinical settings and uses. For example, human-electronics interfaces that employ EMG, such as those proposed in U.S. Pat. Nos. 6,244,873 and 8,170,656, usually employ surface EMG sensors. Surface EMG sensors are available in two forms: resistive EMG sensors and capacitive EMG sensors. The electrode of a resistive EMG sensor is typically directly electrically coupled to the user's skin while the electrode of a capacitive EMG sensor is typically capacitively coupled to the user's skin. That is, for a resistive EMG sensor, the electrode typically comprises a plate of electrically conductive material that is in direct physical contact with the user's skin, while for a capacitive EMG sensor, the electrode typically comprises a plate of electrically conductive material that is electrically insulated from the user's skin by at least one thin intervening layer of dielectric material or cloth.

Resistive EMG sensors and capacitive EMG sensors both have relative advantages and disadvantages. For example, the resistive coupling to the skin realized by a resistive EMG sensor provides a relatively low impedance (compared to a capacitive coupling) between the skin and the sensor and this can greatly simplify the circuitry needed to amplify the detected EMG signals; however, because this resistive coupling is essentially galvanic and uninterrupted, it can also undesirably couple DC voltage to the amplification circuitry and/or result in a voltage applied to the skin of the user. Both of these effects potentially impact the quality of the EMG signals detected. On the other hand, the capacitive coupling to the skin realized by a capacitive EMG sensor galvanically isolates the amplification circuitry from the skin and thereby prevents a DC voltage from coupling to the amplification circuitry and prevents a voltage from being applied to the skin; however, this capacitive coupling provides a relatively high impedance between the skin and the sensor and this can complicate the circuitry needed to amplify the detected EMG signals (thus making the amplification circuitry more expensive). The strength of the capacitive coupling can also vary widely from user to user. Clearly, neither type of surface EMG sensor is ideal and there is a need in the art for improved surface EMG sensor designs.

BRIEF SUMMARY

An electromyography (“EMG”) sensor may be summarized as including a first sensor electrode formed of an electrically conductive material; an amplifier; a first electrically conductive pathway that communicatively couples the first sensor electrode and the amplifier; a first capacitor electrically coupled in series between the first sensor electrode and the amplifier in the first electrically conductive pathway; and a first resistor electrically coupled in series between the first sensor electrode and the amplifier in the first electrically conductive pathway. The first capacitor and the first resistor may be electrically coupled in series with one another in the first electrically conductive pathway. The EMG sensor may further include: a second electrically conductive pathway that communicatively couples to ground; a third electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway; a second capacitor electrically coupled in the third electrically conductive pathway in between the first electrically conductive pathway and the second electrically conductive pathway; a fourth electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway; and a second resistor electrically coupled in the fourth electrically conductive pathway in between the first electrically conductive pathway and the second electrically conductive pathway. The EMG sensor may be a differential EMG sensor that further includes: a second sensor electrode formed of an electrically conductive material; a fifth electrically conductive pathway that communicatively couples the second sensor electrode and the amplifier; a third capacitor electrically coupled in series between the second sensor electrode and the amplifier in the fifth electrically conductive pathway; and a third resistor electrically coupled in series between the second sensor electrode and the amplifier in the fifth electrically conductive pathway. The third capacitor and the third resistor may be electrically coupled in series with one another in the fifth electrically conductive pathway. The EMG sensor may further include: a sixth electrically conductive pathway that communicatively couples the fifth electrically conductive pathway and the second electrically conductive pathway; a fourth capacitor electrically coupled in the sixth electrically conductive pathway in between the fifth electrically conductive pathway and the second electrically conductive pathway; a seventh electrically conductive pathway that communicatively couples the fifth electrically conductive pathway and the second electrically conductive pathway; and a fourth resistor electrically coupled in the seventh electrically conductive pathway in between the fifth electrically conductive pathway and the second electrically conductive pathway. The EMG sensor may further include a ground electrode formed of an electrically conductive material and communicatively coupled to the second electrically conductive pathway.

The first sensor electrode may comprise a first layer formed of a first electrically conductive material and a second layer formed of a second electrically conductive material. The first electrically conductive material may include copper. The second electrically conductive material may include at least one material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, and electrically conductive silicone.

The EMG sensor may further include a housing, wherein the amplifier, the first electrically conductive pathway, the first capacitor, the first resistor, and the first layer of the first sensor electrode are all substantially contained within the housing, the housing including a hole, and wherein at least a portion of the second layer of the first sensor electrode extends out of the housing through the hole. The EMG sensor may further include a substrate having a first surface and a second surface, the second surface opposite the first surface across a thickness of the substrate, wherein the first sensor electrode is carried by the first surface of the substrate and the amplifier, the first capacitor, and the first resistor are all carried by the second surface of the substrate. The first electrically conductive pathway may include at least one via that extends through the substrate. The first electrically conductive pathway may include at least one electrically conductive trace carried by the second surface of the substrate. The first capacitor and the first resistor may include respective discrete electronic components.

A method of fabricating an electromyography (“EMG”) sensor may be summarized as including: forming a first sensor electrode on a first surface of a substrate, wherein forming a first sensor electrode on a first surface of a substrate includes depositing at least a first layer of a first electrically conductive material on the first surface of the substrate; depositing an amplifier on a second surface of the substrate, the second surface opposite the first surface across a thickness of the substrate; depositing a first capacitor on the second surface of the substrate; depositing a first resistor on the second surface of the substrate; and forming a first electrically conductive pathway that communicatively couples the first sensor electrode and the amplifier through the first capacitor and the first resistor. Forming the first electrically conductive pathway may include forming a via through the substrate. Depositing at least a first layer of a first electrically conductive material on the first surface of the substrate may include depositing a first layer including copper on the first surface of the substrate, and forming the first sensor electrode may further include depositing a second layer of a second electrically conductive material on the first layer of the first electrically conductive material, the second electrically conductive material including a material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, and electrically conductive silicone.

The method may further include enclosing the substrate in a housing, wherein the housing includes a hole, and wherein enclosing the substrate in a housing includes enclosing the amplifier, the first capacitor, and the first resistor in the housing and aligning the first sensor electrode with the hole, wherein at least a portion of the second layer of the second electrically conductive material protrudes out of the housing through the hole.

The method may further include forming a ground electrode on the first surface of the substrate; forming a second electrically conductive pathway that communicatively couples to the ground electrode; depositing a second capacitor on the second surface of the substrate; forming a third electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway through the second capacitor; depositing a second resistor on the second surface of the substrate; and forming a fourth electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway through the second resistor. The EMG sensor may be a differential EMG sensor, and the method may further include: forming a second sensor electrode on the first surface of the substrate; depositing a third capacitor on the second surface of the substrate; depositing a third resistor on the second surface of the substrate; and forming a fifth electrically conductive pathway that communicatively couples the second sensor electrode and the amplifier through the third capacitor and the third resistor. The method may further include: depositing a fourth capacitor on the second surface of the substrate; forming a sixth electrically conductive pathway that communicatively couples the fifth electrically conductive pathway and the second electrically conductive pathway through the fourth capacitor; depositing a fourth resistor on the second surface of the substrate; and forming a seventh electrically conductive pathway that communicatively couples the fifth electrically conductive pathway and the second electrically conductive pathway through the fourth resistor.

Depositing the amplifier on the second surface of the substrate may include soldering the amplifier on the second surface of the substrate; depositing the first capacitor on the second surface of the substrate may include soldering the first capacitor on the second surface of the substrate; and/or depositing the first resistor on the second surface of the substrate may include soldering the first resistor on the second surface of the substrate.

A wearable electromyography (“EMG”) device may be summarized as including: at least one EMG sensor responsive to (i.e., to detect and provide at least one signal in response to) muscle activity corresponding to a gesture performed by a user of the wearable EMG device, wherein in response to muscle activity corresponding to a gesture performed by a user the at least one EMG sensor provides signals, and wherein the at least one EMG sensor includes: a first sensor electrode formed of an electrically conductive material; an amplifier; a first electrically conductive pathway that communicatively couples the first sensor electrode and the amplifier; a first capacitor electrically coupled in series between the first sensor electrode and the amplifier in the first electrically conductive pathway; and a first resistor electrically coupled in series between the first sensor electrode and the amplifier in the first electrically conductive pathway; a processor communicatively coupled to the at least one EMG sensor to in use process signals provided by the at least one EMG sensor; and an output terminal communicatively coupled to the processor to transmit signals output by the processor. The at least one EMG sensor may further include: a second electrically conductive pathway that communicatively couples to ground; a third electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway; a second capacitor electrically coupled in between the first electrically conductive pathway and the second electrically conductive pathway in the third electrically conductive pathway; a fourth electrically conductive pathway that communicatively couples the first electrically conductive pathway and the second electrically conductive pathway; and a second resistor electrically coupled in between the first electrically conductive pathway and the second electrically conductive pathway in the fourth electrically conductive pathway. The at least one EMG sensor may include at least one differential EMG sensor, and the at least one differential EMG sensor may further include: a second sensor electrode formed of an electrically conductive material; a fifth electrically conductive pathway that communicatively couples the second sensor electrode and the amplifier; a third capacitor electrically coupled in between the second sensor electrode and the amplifier in the fifth electrically conductive pathway; and a third resistor electrically coupled in between the second sensor electrode and the amplifier in the fifth electrically conductive pathway. The at least one EMG sensor may further include a ground electrode formed of an electrically conductive material and communicatively coupled to the second electrically conductive pathway.

The first sensor electrode of the at least one EMG sensor may comprise a first layer formed of a first electrically conductive material and a second layer formed of a second electrically conductive material. The first electrically conductive material may include copper. The second electrically conductive material may include at least one material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, and electrically conductive silicone. The wearable EMG device may further include: at least one housing that at least partially contains the at least one EMG sensor, wherein the amplifier, the first electrically conductive pathway, the first capacitor, the first resistor, and the first layer of the first sensor electrode are all substantially contained within the at least one housing, the at least one housing including a hole, and wherein at least a portion of the second layer of the first sensor electrode extends out of the at least one housing through the hole.

A capacitive electromyography (“EMG”) sensor may be summarized as including: a first sensor electrode to in use resistively couple to a user's skin, wherein the first sensor electrode includes a plate of electrically conductive material; circuitry communicatively coupled to the first sensor electrode of the capacitive EMG sensor; and a first capacitor to in use galvanically isolate the circuitry from the user's skin, the first capacitor electrically coupled in series between the first sensor electrode and the circuitry. Resistive coupling between the first sensor electrode and the user's skin may include an impedance, and the capacitive EMG sensor may further include a first resistor to in use dominate the impedance of the resistive coupling between the first sensor electrode and the user's skin, wherein the first resistor is electrically coupled in series between the first sensor electrode and the circuitry and wherein the first resistor has a magnitude of at least 1 kΩ. The first resistor may have a magnitude of at least 10 kΩ. The circuitry may include at least a portion of at least one circuit selected from the group consisting of: an amplification circuit, a filtering circuit, and an analog-to-digital conversion circuit. The capacitive EMG sensor may further include a ground electrode to in use resistively couple to the user's skin, wherein the ground electrode includes a plate of electrically conductive material, and wherein the ground electrode is communicatively coupled to the circuitry. The circuitry may include: a high-pass filter that includes the first capacitor and a second resistor; and a low-pass filter that includes the first resistor and a second capacitor.

The first sensor electrode may comprise: a first layer of a first electrically conductive material; and a second layer of a second electrically conductive material. The first electrically conductive material may include copper. The second electrically conductive material may include at least one material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, and electrically conductive silicone. The capacitive EMG sensor may further include a housing, wherein the circuitry, the first capacitor, and the first layer of the first sensor electrode are all substantially contained within the housing, the housing including a hole, and wherein at least a portion of the second layer of the first sensor electrode extends out of the housing through the hole. The capacitive EMG sensor may be a differential capacitive EMG sensor that further includes: a second sensor electrode to in use resistively couple to the user's skin, wherein the second sensor electrode includes a plate of electrically conductive material; and a second capacitor to in use galvanically isolate the circuitry from the user's skin, the second capacitor electrically coupled in series between the second sensor electrode and the circuitry.

A wearable electromyography (“EMG”) device may be summarized as including: at least one capacitive EMG sensor responsive to (i.e., to detect and provide at least one signal in response to detecting) muscle activity corresponding to a gesture performed by a user of the wearable EMG device, wherein in response to muscle activity corresponding to a gesture performed by a user the at least one capacitive EMG sensor provides signals, and wherein the at least one capacitive EMG sensor includes: a first sensor electrode to in use resistively couple to the user's skin, wherein the first sensor electrode includes a plate of electrically conductive material; circuitry communicatively coupled to the first sensor electrode of the capacitive EMG sensor; and a first capacitor to in use galvanically isolate the circuitry from the user's skin, the first capacitor electrically coupled in series between the first sensor electrode and the circuitry; a processor communicatively coupled to the at least one capacitive EMG sensor to in use process signals provided by the at least one capacitive EMG sensor; and an output terminal communicatively coupled to the processor to transmit signals output by the processor

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

FIG. 1 is a schematic diagram of a capacitive EMG sensor that employs sensor electrodes that are configured to capacitively couple to the skin of a user.

FIG. 2 is a schematic diagram of a capacitive EMG sensor employing sensor electrodes that are adapted to, in use, resistively couple to the skin of a user in accordance with the present systems, articles, and methods.

FIG. 3 is a cross sectional view of a capacitive EMG sensor that resistively couples to the user's skin in accordance with the present systems, articles, and methods.

FIG. 4 is a cross sectional view of a capacitive EMG sensor packaged in a housing and employing bi-layer sensor electrodes that protrude from the housing in order to physically contact and electrically couple to a user's skin in accordance with the present systems, articles, and methods.

FIG. 5 is a flow-diagram of a method of fabricating an EMG sensor in accordance with the present systems, articles, and methods.

FIG. 6 is a perspective view of an exemplary wearable EMG device that includes capacitive EMG sensors adapted to, in use, resistively couple to the user's skin in accordance with the present systems, articles, and methods.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with electric circuits, and in particular printed circuit boards, have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its broadest sense, that is as meaning “and/or” unless the content clearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

The various embodiments described herein provide systems, articles, and methods for surface EMG sensors that improve upon existing resistive and capacitive EMG sensor designs. The surface EMG sensors described herein may be understood as hybrid surface EMG sensors that incorporate elements from both resistive EMG sensors and capacitive EMG sensors. In particular, the present systems, articles, and methods describe capacitive EMG sensors that employ at least one sensor electrode that resistively couples to the user's body (e.g., skin) and at least one discrete component capacitor that interrupts the signal path between the at least one sensor electrode and the sensor circuitry. In this way, the capacitive element of the capacitive EMG sensor remains but is essentially moved downstream in the sensor circuit, affording many benefits discussed in detail below. An example application in a wearable EMG device that forms part of a human-electronics interface is also described.

Throughout this specification and the appended claims, the term “capacitive EMG sensor” is used to describe a surface EMG sensor in which communicative coupling between the user's body (e.g., skin) and the sensor circuitry is mediated by at least one capacitive element such that the sensor circuitry is galvanically isolated from the body of the user. In the art, this at least one capacitive element is typically realized at the sensor electrode by configuring the sensor electrode to capacitively couple to the user's skin (e.g., by coating the electrically conductive plate of the sensor electrode with a thin layer of dielectric material). In accordance with the present systems, articles, and methods, the at least one capacitive element may be moved downstream in the sensor such that the sensor electrode resistively/galvanically couples to the user's skin but at least one discrete component capacitor mediates communicative coupling between the sensor electrode and the sensor circuitry.

For comparison purposes, the elements of a capacitive EMG sensor that implements a sensor electrode that capacitively couples to the user's skin are first described.

FIG. 1 is a schematic diagram of a capacitive EMG sensor 100 that employs sensor electrodes 101 a, 101 b that are configured to capacitively couple to the skin of a user. Sensor 100 is a differential capacitive EMG sensor that employs two sensor electrodes 101 a, 101 b as described in, for example, U.S. Provisional Patent Application Ser. No. 61/771,500 (now U.S. Non-Provisional patent application Ser. No. 14/194,252) which is incorporated by reference herein in its entirety. However, a person of skill in the art will appreciate that the basic description of sensor 100 herein is also applicable to single-ended sensor systems that employ only a single sensor electrode (i.e., one of sensor electrodes 101 a or 101 b). Sensor electrodes 101 a and 101 b each comprise a respective electrically conductive plate 171 a, 171 b coated with a respective layer of dielectric material 172 a, 172 b. Sensor 100 also includes a ground electrode 140 that comprises an electrically conductive plate that is exposed (i.e., not coated with dielectric material) so that ground electrode 140 resistively couples to the user's skin as described in U.S. Provisional Patent Application Ser. No. 61/903,238 (now U.S. Non-Provisional patent application Ser. No. 14/539,773), which is incorporated herein by reference in its entirety.

Sensor 100 includes circuitry that comprises, at least: electrically conductive pathways 111 a, 111 b, 112, 113 a, 113 b; resistors 130 a, 130 b; and amplifier 150. First sensor electrode 101 a is communicatively coupled to amplifier 150 through electrically conductive pathway 111 a and to ground electrode 140 through a path that comprises electrically conductive pathway 113 a, resistor 130 a, and electrically conductive pathway 112. Second sensor electrode 101 b is communicatively coupled to amplifier 150 through electrically conductive pathway 111 b and to ground electrode 140 through a path that comprises electrically conductive pathway 113 b, resistor 130 b, and electrically conductive pathway 112.

Sensor 100 is a capacitive EMG sensor in the traditional sense because it implements sensor electrodes 101 a, 101 b that are configured to capacitively couple to the skin of the user. Amplifier 150 is galvanically isolated from the user's skin by the dielectric layers 172 a, 172 b that coat sensor electrodes 101 a, 101 b, respectively. As discussed previously, this galvanic isolation is advantageous, at least because it prevents DC voltage(s) from coupling to amplifier 150 and prevents voltage(s) from being applied to the user's skin. However, the capacitive coupling to the skin through sensor electrodes 101 a, 101 b introduces a relatively large impedance between the user's skin and amplifier 150. This impedance imposes stringent requirements on amplifier 150 and, ultimately, increases the cost of amplifier 150 in sensor 100. Furthermore, the magnitude of the capacitive coupling between sensor electrodes 101 a, 101 b and the user's skin is highly dependent on parameters such as skin conductance, skin moisture/sweat levels, hair density, and so on, all of which can vary considerably from user to user (and even in different scenarios for the same user, such as at different levels of physical activity). Thus, even though the galvanic isolation realized by dielectric layers 172 a and 172 b is desirable in a surface EMG sensor, capacitive coupling between sensor electrodes 101 a, 101 b and the user's skin has undesirable consequences. In accordance with the present systems, articles, and methods, the benefits of galvanically isolating the amplifier (e.g., 150) from the user's skin may be realized without the drawbacks of capacitively coupling the sensor electrode(s) to the user's skin by a capacitive EMG sensor design in which the capacitive interruption between the user's skin and the amplifier is moved downstream in the sensor circuit and realized by a discrete component capacitor coupled in between a resistive sensor electrode and an amplification circuit.

FIG. 2 is a schematic diagram of a capacitive EMG sensor 200 employing sensor electrodes 201 a, 201 b that are adapted to, in use, resistively couple to the body (e.g., skin) of a user in accordance with the present systems, articles, and methods. Each of sensor electrodes 201 a and 201 b comprises a respective plate of electrically conductive material, but unlike electrodes 101 a and 101 b from sensor 100, electrodes 201 a and 201 b are not coated with dielectric material. Instead, each of electrodes 201 a and 201 b includes a respective bare/exposed electrically conductive surface to directly physically contact the user's skin during use. Thus, capacitive EMG sensor 200 implements sensor electrodes 201 a, 201 b that resemble the sensor electrodes that would typically be found in a resistive EMG sensor. However, in accordance with the present systems, articles, and methods, sensor 200 is still a capacitive EMG sensor because sensor 200 includes discrete component capacitors 221 a and 221 b that galvanically isolate the rest of the sensor circuitry from the user's body (e.g., skin).

Sensor 200 is illustrated as a differential capacitive EMG sensor that employs a first sensor electrode 201 a and a second sensor electrode 201 b, though a person of skill in the art will appreciate that the description of sensor 200 herein is also applicable to single-ended sensor systems that employ only a single sensor electrode (i.e., one of sensor electrodes 201 a or 201 b).

Sensor 200 includes an amplification circuit (i.e., an amplifier) 250. First sensor electrode 201 a is communicatively coupled to amplifier 250 by a first electrically conductive pathway 211 a. A first capacitor 221 a is electrically coupled in series between first sensor electrode 201 a and amplifier 250 in first electrically conductive pathway 211 a. First capacitor 221 a galvanically isolates amplifier 250 from the user's body (e.g., skin) and thereby affords some of the benefits typically associated with a capacitive EMG sensor (i.e., capacitor 221 a prevents DC voltage(s) from coupling to amplifier 250 and prevents voltage(s) from being applied to the user's skin). While a traditional capacitive EMG sensor achieves this galvanic isolation by capacitively coupling to the user's skin at the sensor electrode (e.g., as per sensor electrode 101 a from sensor 100), in sensor 200 electrode 201 a is resistively coupled to the user's skin and galvanic isolation is moved downstream to discrete component capacitor 221 a. As previously described, resistive coupling to the user's skin as per electrode 201 a from sensor 200 provides a lower impedance between the user's skin and amplifier 250 than capacitive coupling to the user's skin as in electrode 101 a from sensor 100, and this lower impedance simplifies and lowers the cost of amplifier 250 in sensor 200 compared to amplifier 150 in sensor 100. Furthermore, because capacitor 221 a is a discrete component, the magnitude of its capacitance can be selected and will remain essentially constant from user to user, regardless of variations such as skin conductance, moisture/sweat levels, hair density, and so on. An example implementation may employ, as capacitors 221 a (and similarly as capacitor 221 b), a discrete component capacitor having a magnitude of about 100 nF. Typical capacitive coupling between a dielectric-coated cEMG sensor and a user's skin is significantly less than this, thus 100 nF may dominate the range of variations in skin:electrode capacitance typically seen in cEMG across different users and/or use conditions. The incorporation of a discrete component capacitor 221 a in lieu of condition-dependent capacitive coupling between the electrode and the user's skin is very easy and inexpensive to manufacture and provides an essentially fixed capacitance to which the rest of the sensor circuitry may be tuned for improved performance.

In addition to first capacitor 221 a, sensor 200 also includes a first resistor 231 a that is electrically coupled in series between first sensor electrode 201 a and amplifier 250 in first electrically conductive pathway 211 a. Similar to first capacitor 221 a, first resistor 231 a may be a discrete electronic component with a magnitude that can be selected, accurately embodied, and held substantially constant during use. In the illustrated example of FIG. 2 , first capacitor 221 a and first resistor 231 a are electrically coupled in series with one another in first electrically conductive pathway 211 a. First resistor 231 a is included, at least in part, to dominate the impedance between electrode 201 a and the user's skin such that variations in the impedance between electrode 201 a and the user's skin due to fluctuations in skin and/or environmental conditions (e.g., skin conductance, moisture/sweat levels, hair density, etc.) are rendered essentially negligible. For example, fluctuations in skin and/or environmental conditions may cause the impedance between electrode 201 a and the user's skin to vary by a magnitude of on the order of 10, 100, 1000, or 10000, but first resistor 231 a may be selected to have a resistance of on the order of at least 1 kΩ, at least 10 kΩ, at least 100 kΩ, or more such that the impedance of first resistor 231 a dominates the impedance (and, more specifically, dominates variations in the impedance) between sensor electrode 201 a and the user's skin. The sensor circuitry, including amplifier 250, may be tuned to accommodate the relatively large impedance of first resistor 231 a such that the relatively small variations in the impedance between sensor electrode 201 a and the user's skin from user to user (and/or under different use conditions for the same user) have a diminished effect on the performance of sensor 200. First resistor 231 a also serves to limit current into amplifier 250 and thereby improves the ESD protection of amplifier 250.

The amplifier(s) used in the capacitive EMG sensors described herein may include one or more of various types of amplifier(s), including one or more instrumentation amplifier(s) and/or one or more single or dual operational amplifier(s), depending, for example, on whether the EMG sensor is single-ended or differential. As sensor 200 is differential, amplifier 250 may include a dual operational amplifier (e.g., a “two-op-amp instrumentation amplifier”) such as the MAX9916 or the MAX9917, both available from Maxim Integrated, or any of various other amplifier configurations, including but not limited to amplifiers embodied in integrated circuits. A person of skill in the art will appreciate that the output(s) and/or some of the inputs of amplifier 250 may be connected through various resistor configurations for at least the purpose of determining the gain of amplifier 250.

Sensor 200 includes a second electrically conductive pathway 212 that communicatively couples to ground through a ground electrode 240. Ground electrode 240 comprises a plate of electrically conductive material that resistively couples to the user's skin. As sensor 200 is differential, ground electrode 240 may not necessarily be used as a reference potential but may primarily provide a path for electrical currents to return to the user's body (e.g., skin). Using second electrically conductive pathway 212, together with first capacitor 221 a and first resistor 231 a, circuitry connected to first sensor electrode 201 a also includes both a low-pass filtering configuration and a high-pass filtering configuration “in front of” or upstream of amplifier 250 in a direction in which signals pass. Specifically, sensor 200 includes a third electrically conductive pathway 213 a that communicatively couples first electrically conductive pathway 211 a and second electrically conductive pathway 212. Third electrically conductive pathway 213 a includes a second capacitor 222 a electrically coupled in between first electrically conductive pathway 211 a and second electrically conductive pathway 212. The configuration of first resistor 231 a and second capacitor 222 a (with respect to sensor electrode 201 a, amplifier 250, and ground electrode 240) forms a low-pass filtering circuit. As an example, when first resistor 231 a has a magnitude of about 100 kΩ, second capacitor 222 a may have a magnitude of about 10 pF in order to provide desirable low-pass filtering performance. Similarly, sensor 200 includes a fourth electrically conductive pathway 214 a that communicatively couples first electrically conductive pathway 211 a and second electrically conductive pathway 212. Fourth electrically conductive pathway 214 a includes a second resistor 232 a electrically coupled in between first electrically conductive pathway 211 a and second electrically conductive pathway 212. The configuration of first capacitor 221 a and second resistor 232 a (with respect to sensor electrode 201 a, amplifier 250, and ground electrode 240) forms a high-pass filtering circuit.

In comparing sensor 200 from FIG. 2 to sensor 100 from FIG. 1 , second resistor 232 a in sensor 200 is similar in position and function to resistor 130 a in sensor 100. The magnitude of a resistor in this position (i.e., the magnitude of second resistor 232 a in sensor 200 or resistor 130 a in sensor 100) directly influences the filtering performance of the corresponding high-pass filter; however, as the magnitude of a resistor in this position increases, the stability of the circuit may degrade and more noise may appear. This introduces a further benefit of first capacitor 221 a in sensor 200: first capacitor 221 a compensates for a decrease in the magnitude of second resistor 232 a and thereby allows a lower-magnitude resistor to be used for second resistor 232 a in sensor 200 compared to resistor 130 a in sensor 100. The lower magnitude of second resistor 232 a in sensor 200 compared to resistor 130 a in sensor 100 results in both reduced noise and enhanced stability in sensor 200 compared to sensor 100. As an example, second resistor 232 a may have a magnitude of about 10 MΩ or less (e.g., about 1 MΩ) and first capacitor 221 a may have a magnitude of about 100 nF.

As previously described, the illustrated example in FIG. 2 of capacitive EMG sensor 200 is a differential capacitive EMG sensor. To this end, sensor 200 includes: a second sensor electrode 201 b that is substantially similar to first sensor electrode 201 a; a fifth electrically conductive pathway 211 b (analogous to first electrically conductive pathway 211 a) that communicatively couples second sensor electrode 201 b to amplifier 250; a third capacitor 221 b (analogous to first capacitor 221 a) electrically coupled in series between second sensor electrode 201 b and amplifier 250 in fifth electrically conductive pathway 211 b; and a third resistor 231 b (analogous to first resistor 231 a) electrically coupled in series between second sensor electrode 201 b and amplifier 250 in fifth electrically conductive pathway 211 b. In the illustrated example of FIG. 2 , third capacitor 221 b and third resistor 231 b are electrically coupled in series with one another in fifth electrically conductive pathway 211 b. Third capacitor 221 b may be substantially similar to first capacitor 221 a and third resistor 231 b may be substantially similar to first resistor 231 a. Sensor 200 also includes: a sixth electrically conductive pathway 213 b (analogous to third electrically conductive pathway 213 a) that communicatively couples fifth electrically conductive pathway 211 b and second electrically conductive pathway 212; a fourth capacitor 222 b (analogous to third capacitor 222 a) electrically coupled in sixth electrically conductive pathway 213 b in between fifth electrically conductive pathway 211 b and second electrically conductive pathway 212; a seventh electrically conductive pathway 214 b (analogous to fourth electrically conductive pathway 214 a) that communicatively couples fifth electrically conductive pathway 211 b and second electrically conductive pathway 212; and a fourth resistor 232 b (analogous to second resistor 232 a) electrically coupled in seventh electrically conductive pathway 214 b in between fifth electrically conductive pathway 211 b and second electrically conductive pathway 212. Third capacitor 221 b and fourth resistor 232 b form a high-pass filter configuration with respect to sensor electrode 201 b, amplifier 250, and ground electrode 240 while third resistor 231 b and fourth capacitor 222 b form a low-pass filter configuration with respect to sensor electrode 201 b, amplifier 250, and ground electrode 240. Fourth capacitor 222 b may be substantially similar to second capacitor 222 a and fourth resistor 232 b may be substantially similar to second resistor 232 a.

The various examples of capacitive EMG sensors described herein, including sensor 200 from FIG. 2 , may be formed as a printed circuit board, formed as an integrated circuit, or otherwise carried by a substrate. In this case, one or more electrically conductive pathways (e.g., electrically conductive pathways 211 a, 211 b, 212, 213 a, 213 b, 214 a, and/or 214 b) may be embodied by one or more electrically conductive trace(s) carried by a substrate and formed using one or more lithography process(es).

FIG. 3 is a cross sectional view of a capacitive EMG sensor 300 that resistively couples to the user's skin in accordance with the present systems, articles, and methods. Sensor 300 is an example of a physical embodiment of the schematic diagram for sensor 200 shown in FIG. 2 . Sensor 300 includes elements of sensor 200 and, in general, the descriptions of the elements of sensor 200 apply to the analogous elements in sensor 300 and vice versa.

Sensor 300 includes a substrate 360 formed of an insulating material (e.g., FR-4) and having a first surface 360 a and a second surface 360 b. Second surface 360 b is opposite first surface 360 a across a thickness of substrate 360. Sensor 300 is a differential EMG sensor comprising two sensor electrodes 30 a, 301 b (analogous to sensor electrodes 201 a, 201 b of sensor 200), both carried by first surface 360 a of substrate 360. The circuitry that comprises the other elements of sensor 300 (e.g., an amplifier 350 analogous to amplifier 250 of sensor 200, capacitors 321 a, 321 b analogous to capacitors 221 a, 221 b of sensor 200, and resistors 331 a, 331 b analogous to resistors 231 a, 231 b of sensor 200) is carried by second surface 360 b of substrate 360 and communicatively coupled to electrodes 301 a, 301 b by electrically conductive pathways 311 a, 311 b (analogous to electrically conductive pathways 211 a, 211 b of sensor 200), which include via portions that extend through the thickness of substrate 360 and electrically conductive trace portions that are carried by second surface 360 b of substrate 360.

Throughout this specification and the appended claims, the terms “carries” and “carried by” are generally used to describe a spatial relationship in which a first layer/component is positioned proximate and physically coupled to a surface of a second layer/component, either directly or through one or more intervening layers/components. For example, electrode 301 a is carried by first surface 360 a of substrate 360 and amplifier 350 is carried by second surface 360 b of substrate 360. Amplifier 350 is directly carried by second surface 360 b of substrate 360 because there are no intervening layers/components that mediate the physical coupling between amplifier 350 and second surface 360 b of substrate 360; however, amplifier 350 would still be considered “carried by” second surface 360 b of substrate 360 even if the physical coupling between amplifier 350 and second surface 360 b of substrate 360 was mediated by at least one intervening layer/component. The terms “carries” and “carried by” are not intended to denote a particular orientation with respect to top and bottom and/or left and right.

Each resistive sensor electrode of the capacitive EMG sensors described herein (e.g., electrodes 301 a, 301 b of sensor 300) comprises a respective electrically conductive plate that physically and electrically (i.e., galvanically/resistively) couples to the user's skin during use. For each such sensor electrode, the electrically conductive plate may be formed of, for example, a material that includes copper (such as pure elemental copper or a copper alloy), deposited and etched in accordance with established lithography techniques. While copper is an excellent material from which to form sensor electrodes 301 a, 301 b from a manufacturing point of view (because lithography techniques for processing copper are very well established in the art), an exposed surface of pure copper will ultimately form an insulating oxide layer and/or react with the skin of a user in other undesirable ways. This effect may be acceptable for traditional capacitive sensor electrodes that capacitively couple to the user because, as described previously, such electrodes are typically coated with an insulating dielectric layer anyway. However, the formation of such an insulating layer can undesirably effect the operation of a sensor electrode that resistively couples to the user's skin. In some cases, a user's skin may even react with copper, resulting in a rash or other discomfort for the user. For at least these reasons, in accordance with the present systems, articles, and methods it can be advantageous to form each of sensor electrodes 301 a, 301 b (and likewise electrodes 201 a and 201 b of FIG. 2 ) as a respective multilayer (e.g., bi-layer) structure comprising a first layer 371 a, 371 b formed of a first electrically conductive material (e.g., copper or a material including copper) and at least a second layer 372 a, 372 b formed of a second electrically conductive material. In accordance with the present systems, articles, and methods, the second electrically conductive material may be an inert, non-reactive, and/or biocompatible material. For example, the second electrically conductive material may include: gold, steel (e.g., a stainless steel such as a 316 stainless steel or a low-nickel stainless steel to mitigate dermatological nickel allergies, such as 430 stainless steel), silver, titanium, electrically conductive rubber, and/or electrically conductive silicone.

The use of multilayer (e.g., bi-layer) structures for sensor electrodes 301 a, 301 b is advantageous because it enables the first layer 371 a, 371 b to be formed of copper using established lithography techniques and the second layer 372 a, 372 b to be subsequently applied in order to protect the copper from exposure to the user/environment and to protect the user from exposure to the copper. Furthermore, an EMG sensor (e.g., sensor 300) may be packaged in a housing for both protective and aesthetic purposes, and a second layer 372 a, 372 b of electrically conductive material may be used to effectively increase the thickness of sensor electrodes 301 a, 301 b such that they protrude outwards from the housing to resistively couple to the user's skin during use.

FIG. 4 is a cross sectional view of a capacitive EMG sensor 400 packaged in a housing 490 and employing bi-layer sensor electrodes 401 a, 401 b that protrude from the housing in order to physically contact and electrically (i.e., resistively/galvanically) couple to a user's skin in accordance with the present systems, articles, and methods. Sensor 400 is substantially similar to sensor 300 from FIG. 3 and includes the same or similar elements (e.g., a substrate 460 having a first surface 460 a and a second surface 460 b, where first surface 460 a carries first and second sensor electrodes 401 a, 401 b and second surface 460 b carries an amplifier 450, first and second capacitors 421 a, 421 b, first and second resistors 431 a, 431 b, etc.), all at least partially contained within the inner volume of a housing 490. Housing 490 may be formed of substantially rigid material. Throughout this specification and the appended claims, the term “rigid” as in, for example, “substantially rigid material,” is used to describe a material that has an inherent tendency to maintain or restore its shape and resist malformation/deformation under, for example, the moderate stresses and strains typically encountered by a wearable electronic device.

Bi-layer sensor electrodes 401 a, 401 b are similar to bi-layer sensor electrodes 301 a, 301 b of sensor 300 in that they each comprise a respective first layer 471 a, 471 b formed of a first electrically conductive material (e.g., copper, or a material including copper) and a respective second layer 472 a, 472 b formed of a second electrically conductive material (e.g., gold, steel, stainless steel, conductive rubber, etc.); however, in sensor 400 the respective second layer 472 a, 472 b of each of electrodes 401 a, 401 b is substantially thicker than the respective first layer 471 a, 471 b of each of electrodes 401 a, 401 b. At least two holes 480 a, 480 b in housing 490 provide access to the inner volume of housing 490, and the thickness of second layers 472 a, 472 b of electrodes 401 a, 401 b (respectively) is sufficient such that at least respective portions of second layers 472 a, 472 b protrude out of housing 490 through holes 480 a, 480 b. More specifically, first sensor electrode 401 a includes a first layer 471 a and a second layer 472 a, housing 490 includes a first hole 480 a, and at least a portion of second layer 472 a of first sensor electrode 401 a extends out of housing 490 through first hole 480 a. Likewise, second sensor electrode 401 b includes a first layer 471 b and a second layer 472 b, housing 490 includes a second hole 480 b, and at least a portion of second layer 472 b of second sensor electrode 401 b extends out of housing 490 through second hole 480 b. In this way, housing 490 protects sensor 400 from the elements and affords opportunities to enhance aesthetic appeal, while the protruding portions of second layers 472 a, 472 b of sensor electrodes 401 a, 401 b are still able to resistively couple to the skin of the user during use. Housing 490 also helps to electrically insulate electrodes 401 a, 401 b from one another. In some applications, it can be advantageous to seal any gap between the perimeter of first hole 480 a and the protruding portion of second layer 472 a of first electrode 401 a (using, e.g., a gasket, an epoxy or other sealant or, in the case of electrically conductive rubber or electrically conductive silicone as the material forming second layer 472 a of first electrode 401 a, a tight interference fit between the perimeter of first hole 480 a and the protruding portion of second layer 472 a of first electrode 401 a) to prevent moisture or contaminants from entering housing 490. Likewise, it can be advantageous to seal any gap between the perimeter of second hole 480 b and the protruding portion of second layer 472 b of second electrode 401 b.

As previously described, the various embodiments of capacitive EMG sensors described herein may include at least one ground electrode. For example, sensor 200 from FIG. 2 depicts ground electrode 240. Sensor 300 from FIG. 3 and sensor 400 from FIG. 4 each do not illustrate a ground electrode for two reasons: a) to reduce clutter; and b) because in various embodiments, a ground electrode may or may not be carried by the same substrate as the sensor electrode(s). Sensor electrodes (such as electrodes 201 a, 201 b, 301 a, 301 b, and 401 a, 401 b) are advantageously positioned near muscle groups in order to detect EMG signals therefrom, but in some applications it is advantageous for ground electrodes (such as electrode 240) to be positioned distant from the sensor electrodes and/or near bone instead of near muscle groups. For this reason, one or more ground electrode(s) may, in some applications, be separate from the substrate which carries the sensor electrodes but still communicatively coupled to the sensor circuitry by one or more electrically conductive pathways (e.g., electrical wires). However, in some applications one or more ground electrode(s) may be carried by the same substrate that carries the sensor electrodes, at least in part because doing so greatly simplifies the design and manufacture of the EMG sensor. For example, sensor 300 from FIG. 3 may further include a ground electrode carried by first surface 360 a of substrate 360 and/or sensor 400 from FIG. 4 may further include a ground electrode carried by first surface 460 a of substrate 460. In either case, the ground electrode may comprise a first layer formed of a first electrically conductive material (e.g., copper, or a material including copper) and a second layer formed of a second electrically conductive material (e.g., gold, steel, stainless steel, electrically conductive rubber, etc.). In applications that employ a housing, such as housing 490 of sensor 400, the housing may include a hole (e.g., a third hole) and at least a portion of the second layer of the ground electrode may protrude through the hole to physically contact and electrically (i.e., resistively/galvanically) couple to the skin of the user during use.

In accordance with the present systems, articles, and methods, multilayer (e.g., bi-layer) electrodes, including multilayer sensor electrodes and/or multilayer ground electrodes, may be formed by, for example: electroplating a second layer of electrically conductive material on a first layer of electrically conductive material; depositing a second layer of electrically conductive material on a first layer of electrically conductive material using deposition or growth techniques such as chemical vapor deposition, physical vapor deposition thermal oxidation, or epitaxy; adhering a second layer of electrically conductive material to a first layer of electrically conductive material using, for example, an electrically conductive epoxy or an electrically conductive solder; pressing a second layer of electrically conductive material against a first layer of electrically conductive material using, for example, an interference fit, one or more spring(s), or one or more elastic band(s); or otherwise generally bonding a second electrically conductive material to a first electrically conductive material in such a way that the second electrically conductive material is electrically coupled to the first electrically coupled material.

FIG. 5 is a flow-diagram of a method 500 of fabricating an EMG sensor in accordance with the present systems, articles, and methods. Method 500 includes five acts 501, 502, 503, 504, and 505, though those of skill in the art will appreciate that in alternative embodiments certain acts may be omitted and/or additional acts may be added. Those of skill in the art will also appreciate that the illustrated order of the acts is shown for exemplary purposes only and may change in alternative embodiments.

At 501, a first sensor electrode is formed on a first surface of a substrate. The first sensor electrode may comprise an electrically conductive plate such as for example electrode 301 a of sensor 300 or electrode 401 a of sensor 400, formed using, as an example, lithography techniques. The first sensor electrode may include a single layer of electrically conductive material or multiple (i.e., at least two) layers of one or more electrically conductive material(s). Forming the first sensor electrode may therefore include depositing at least a first layer of a first electrically conductive material (e.g., copper) on the first surface of the substrate. Where, in accordance with the present systems, articles, and methods, it is desirable for the first sensor electrode to comprise multiple layers, forming the first sensor electrode may further include depositing a second layer of a second electrically conductive material (e.g., gold, steel, stainless steel, electrically conductive rubber, etc.) on the first layer of the first electrically conductive material (either directly by, for example, a plating process or indirectly by, for example, employing an intervening adhesive layer such as an electrically conductive epoxy or an electrically conductive solder).

At 502, an amplifier (e.g., amplifier 250 of sensor 200, amplifier 350 of sensor 300, or amplifier 450 of sensor 400) is deposited on a second surface of the substrate. The amplifier may include an amplification circuit and/or one or more discrete electronic component amplifier(s), such as for example on or more operational amplifier(s), differential amplifier(s), and/or instrumentation amplifier(s). Depositing the amplifier on the second surface of the substrate may include soldering a discrete component amplifier to one or more electrically conductive trace(s) and/or bonding pad(s) carried by the second surface of the substrate (i.e., soldering the amplifier on the second surface of the substrate using, for example, a surface-mount technology, or “SMT,” process).

At 503, a first capacitor (e.g., capacitor 221 a of sensor 200, capacitor 321 a of sensor 300, or capacitor 421 a of sensor 400) is deposited on the second surface of the substrate. The first capacitor may include a discrete electronic component capacitor and depositing the first capacitor on the second surface of the substrate may include soldering the first capacitor to one or more electrically conductive trace(s) and/or bonding pad(s) carried by the second surface of the substrate (i.e., soldering the first capacitor on the second surface of the substrate using, for example, a SMT process).

At 504, a first resistor (e.g., resistor 231 a of sensor 200, resistor 331 a of sensor 300, or resistor 431 a of sensor 400) is deposited on the second surface of the substrate. The first resistor may include a discrete electronic component resistor and depositing the first resistor on the second surface of the substrate may include soldering the first resistor to one or more electrically conductive trace(s) and/or bonding pad(s) carried by the second surface of the substrate (i.e., soldering the first resistor on the second surface of the substrate using, for example, a SMT process).

As described previously, a person of skill in the art will appreciate that the order of the acts in method 500, and in particular the order of acts 501, 502, 503, and 504, is provided as an example only and in practice acts 501, 502, 503, and 504 may be carried out in virtually any order or combination, and any/all of acts 501, 502, 503, and 504 may be carried out substantially concurrently or even simultaneously (in, for example, an SMT process).

At 505, a first electrically conductive pathway (e.g., pathway 211 a of sensor 200 or pathway 311 a of sensor 300) that communicatively couples the first sensor electrode to the amplifier through the first capacitor and the first resistor is formed. The first electrically conductive pathway may include one or more section(s) of electrically conductive trace carried by the second surface of the substrate and at least one via that electrically couples at least one of the one or more section(s) of electrically conductive trace to the first sensor electrode carried by the first surface of the substrate. Thus, forming the first electrically conductive pathway may employ established lithography techniques to form the one or more section(s) of electrically conductive trace and to form a via through the substrate.

As previously described, the EMG sensor may include or otherwise be packaged in a housing, such as housing 490 of sensor 400. In this case, method 500 may be extended to include enclosing the substrate in a housing. Enclosing the substrate in the housing includes enclosing the amplifier, the first capacitor, and the first resistor in the housing. The housing may include a hole providing access to the inner volume thereof, and enclosing the substrate in the housing may include aligning the first sensor electrode with the hole so that at least a portion of the first senor electrode protrudes out of the housing through the hole. For implementations in which the first sensor electrode comprises a first layer and a second layer, aligning the first sensor electrode with the hole may include aligning the first sensor electrode with the hole so that at least a portion of the second layer protrudes out of the housing through the hole.

As previously described, the EMG sensor may include a ground electrode. For example, sensor 200 from FIG. 2 includes ground electrode 240. In order to include a ground electrode (240) and associated circuitry in an EMG sensor, method 500 may be extended to include: forming the ground electrode (240) on the first surface of the substrate; forming a second electrically conductive pathway (212) that communicatively couples to the ground electrode (240); depositing a second capacitor (222 a) on the second surface of the substrate; forming a third electrically conductive pathway (213 a) that communicatively couples the first electrically conductive pathway (211 a) and the second electrically conductive pathway (212) through the second capacitor (222 a); depositing a second resistor (232 a) on the second surface of the substrate; and forming a fourth electrically conductive pathway (214 a) that communicatively couples the first electrically conductive pathway (211 a) and the second electrically conductive pathway (212) through the second resistor (232 a). Forming the ground electrode and the second, third, and fourth electrically conductive pathways may employ established lithography processes. Depositing the second capacitor and the second resistor may involve soldering discrete circuit components on the substrate (e.g., using a SMT process).

With or without a ground electrode (240), the EMG sensor may be differential. For example, sensor 200 from FIG. 2 includes second sensor electrode 201 b. In order to include a second sensor electrode (201 b) and associated circuitry in an EMG sensor, method 500 may be extended to include: forming a second sensor electrode (201 b) on the first surface of the substrate; depositing a third capacitor (221 b) on the second surface of the substrate; depositing a third resistor (231 b) on the second surface of the substrate; and forming a fifth electrically conductive pathway (211 b) that communicatively couples the second sensor electrode (201 b) and the amplifier (250) through the third capacitor (221 b) and the third resistor (231 b). Forming the second sensor electrode and the fifth electrically conductive pathway may employ established lithography processes. Depositing the third capacitor and the third resistor may involve soldering discrete circuit components on the substrate (e.g., using a SMT process). For a differential EMG sensor that includes a ground electrode (e.g., as in sensor 200 from FIG. 2 ), method 500 may be extended to include: depositing a fourth capacitor (222 b) on the second surface of the substrate; forming a sixth electrically conductive pathway (213 b) that communicatively couples the fifth electrically conductive pathway (211 b) and the second electrically conductive pathway (212) through the fourth capacitor (222 b); depositing a fourth resistor (232 b) on the second surface of the substrate; and forming a seventh electrically conductive pathway (214 b) that communicatively couples the fifth electrically conductive pathway (211 b) and the second electrically conductive pathway (212) through the fourth resistor (232 b). Forming the sixth and seventh electrically conductive pathways may employ established lithography processes. Depositing the fourth capacitor and the fourth resistor may involve soldering discrete circuit components on the substrate (e.g., using a SMT process).

Capacitive EMG sensors having sensor electrodes that resistively couple to the user's skin as described herein may be implemented in virtually any system, device, or process that makes use of capacitive EMG sensors; however, the capacitive EMG sensors described herein are particularly well-suited for use in EMG devices that are intended to be worn by (or otherwise coupled to) a user for an extended period of time and/or for a range of different skin and/or environmental conditions. As an example, the capacitive EMG sensors described herein may be implemented in a wearable EMG device that provides gesture-based control in a human-electronics interface. Some details of exemplary wearable EMG devices that may be adapted to include at least one capacitive EMG sensor from the present systems, articles, and methods are described in, for example, U.S. Provisional Patent Application Ser. No. 61/768,322 (now U.S. Non-Provisional patent application Ser. No. 14/186,889); U.S. Provisional Patent Application Ser. No. 61/857,105 (now U.S. Non-Provisional patent application Ser. No. 14/335,668); U.S. Provisional Patent Application Ser. No. 61/860,063 (now U.S. Non-Provisional patent application Ser. No. 14/276,575); U.S. Provisional Patent Application Ser. No. 61/866,960 (now U.S. Non-Provisional patent application Ser. No. 14/461,044); U.S. Provisional Patent Application Ser. No. 61/869,526 (now U.S. Non-Provisional patent application Ser. No. 14/465,194); U.S. Provisional Patent Application Ser. No. 61/881,064 (now U.S. Non-Provisional patent application Ser. No. 14/494,274); and U.S. Provisional Patent Application Ser. No. 61/894,263 (now U.S. Non-Provisional patent application Ser. No. 14/520,081), all of which are incorporated herein by reference in their entirety.

Throughout this specification and the appended claims, the term “gesture” is used to generally refer to a physical action (e.g., a movement, a stretch, a flex, a pose, etc.) performed or otherwise effected by a user. Any physical action performed or otherwise effected by a user that involves detectable muscle activity (detectable, e.g., by at least one appropriately positioned EMG sensor) may constitute a gesture in the present systems, articles, and methods.

FIG. 6 is a perspective view of an exemplary wearable EMG device 600 that includes capacitive EMG sensors adapted to, in use, resistively couple to the user's skin in accordance with the present systems, articles, and methods. Exemplary wearable EMG device 600 may, for example, form part of a human-electronics interface. Exemplary wearable EMG device 600 is an armband designed to be worn on the forearm of a user, though a person of skill in the art will appreciate that the teachings described herein may readily be applied in wearable EMG devices designed to be worn elsewhere on the body of the user, including without limitation: on the upper arm, wrist, hand, finger, leg, foot, torso, or neck of the user.

Device 600 includes a set of eight pod structures 601, 602, 603, 604, 605, 606, 607, and 608 that form physically coupled links of the wearable EMG device 600. Each pod structure in the set of eight pod structures 601, 602, 603, 604, 605, 606, 607, and 608 is positioned adjacent and in between two other pod structures in the set of eight pod structures such that the set of pod structures forms a perimeter of an annular or closed loop configuration. For example, pod structure 601 is positioned adjacent and in between pod structures 602 and 608 at least approximately on a perimeter of the annular or closed loop configuration of pod structures, pod structure 602 is positioned adjacent and in between pod structures 601 and 603 at least approximately on the perimeter of the annular or closed loop configuration, pod structure 603 is positioned adjacent and in between pod structures 602 and 604 at least approximately on the perimeter of the annular or closed loop configuration, and so on. Each of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 is physically coupled to the two adjacent pod structures by at least one adaptive coupler (not visible in FIG. 6 ). For example, pod structure 601 is physically coupled to pod structure 608 by an adaptive coupler and to pod structure 602 by an adaptive coupler. The term “adaptive coupler” is used throughout this specification and the appended claims to denote a system, article or device that provides flexible, adjustable, modifiable, extendable, extensible, or otherwise “adaptive” physical coupling. Adaptive coupling is physical coupling between two objects that permits limited motion of the two objects relative to one another. An example of an adaptive coupler is an elastic material such as an elastic band. Thus, each of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 in the set of eight pod structures may be adaptively physically coupled to the two adjacent pod structures by at least one elastic band. The set of eight pod structures may be physically bound in the annular or closed loop configuration by a single elastic band that couples over or through all pod structures or by multiple separate elastic bands that couple between adjacent pairs of pod structures or between groups of adjacent pairs of pod structures. Device 600 is depicted in FIG. 6 with the at least one adaptive coupler completely retracted and contained within the eight pod structures 601, 602, 603, 604, 605, 606, 607, and 608 (and therefore the at least one adaptive coupler is not visible in FIG. 6 ).

Throughout this specification and the appended claims, the term “pod structure” is used to refer to an individual link, segment, pod, section, structure, component, etc. of a wearable EMG device. For the purposes of the present systems, articles, and methods, an “individual link, segment, pod, section, structure, component, etc.” (i.e., a “pod structure”) of a wearable EMG device is characterized by its ability to be moved or displaced relative to another link, segment, pod, section, structure component, etc. of the wearable EMG device. For example, pod structures 601 and 602 of device 600 can each be moved or displaced relative to one another within the constraints imposed by the adaptive coupler providing adaptive physical coupling therebetween. The desire for pod structures 601 and 602 to be movable/displaceable relative to one another specifically arises because device 600 is a wearable EMG device that advantageously accommodates the movements of a user and/or different user forms. As described in more detail later on, each of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 may correspond to a respective housing (e.g., housing 490 of sensor 400) of a respective capacitive EMG sensor adapted to, in use, resistively couple to the user's skin in accordance with the present systems, articles, and methods.

Device 600 includes eight pod structures 601, 602, 603, 604, 605, 606, 607, and 608 that form physically coupled links thereof. Wearable EMG devices employing pod structures (e.g., device 600) are used herein as exemplary wearable EMG device designs, while the present systems, articles, and methods may be applied to wearable EMG devices that do not employ pod structures (or that employ any number of pod structures). Thus, throughout this specification, descriptions relating to pod structures (e.g., functions and/or components of pod structures) should be interpreted as being applicable to any wearable EMG device design, even wearable EMG device designs that do not employ pod structures (except in cases where a pod structure is specifically recited in a claim).

In exemplary device 600 of FIG. 6 , each of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 comprises a respective housing, with each housing being akin to a respective one of housing 490 from sensor 400. Each housing may comprise substantially rigid material that encloses a respective inner volume. Details of the components contained within the housings (i.e., within the inner volumes of the housings) of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 are not necessarily visible in FIG. 6 (e.g., the housings may be formed of material that is optically opaque). To facilitate descriptions of exemplary device 600, some internal components are depicted by dashed lines in FIG. 6 to indicate that these components are contained in the inner volume(s) of housings and may not normally be actually visible in the view depicted in FIG. 6 , unless a transparent or translucent material is employed to form the housings. For example, any or all of pod structures 601, 602, 603, 604, 605, 606, 607, and/or 608 may include circuitry (i.e., electrical and/or electronic circuitry). In FIG. 6 , a first pod structure 601 is shown containing circuitry 611 (i.e., circuitry 611 is contained in the inner volume of the housing of pod structure 601), a second pod structure 602 is shown containing circuitry 612, and a third pod structure 608 is shown containing circuitry 618. The circuitry in any or all pod structures may be communicatively coupled to the circuitry in at least one other pod structure by at least one communicative pathway (e.g., by at least one electrically conductive pathway and/or by at least one optical pathway). For example, FIG. 6 shows a first set of communicative pathways 621 providing communicative coupling between circuitry 618 of pod structure 608 and circuitry 611 of pod structure 601, and a second set of communicative pathways 622 providing communicative coupling between circuitry 611 of pod structure 601 and circuitry 612 of pod structure 602.

Throughout this specification and the appended claims the term “communicative” as in “communicative pathway,” “communicative coupling,” and in variants such as “communicatively coupled,” is generally used to refer to any engineered arrangement for transferring and/or exchanging information. Exemplary communicative pathways include, but are not limited to, electrically conductive pathways (e.g., electrically conductive wires, electrically conductive traces), magnetic pathways (e.g., magnetic media), and/or optical pathways (e.g., optical fiber), and exemplary communicative couplings include, but are not limited to, electrical couplings, magnetic couplings, and/or optical couplings.

Each individual pod structure within a wearable EMG device may perform a particular function, or particular functions. For example, in device 600, each of pod structures 601, 602, 603, 604, 605, 606, and 607 includes a respective capacitive EMG sensor 610 (akin to sensor 200 from FIG. 2 , sensor 300 from FIG. 3 , and/or sensor 400 from FIG. 4 ; only one called out in FIG. 6 to reduce clutter) adapted to, in use, resistively couple to the user's skin in accordance with the present systems, articles, and methods. Each capacitive EMG sensor 610 is responsive to muscle activity of the user, meaning that each capacitive EMG sensor 610 included in device 600 to detect muscle activity of a user and to provide electrical signals in response to the detected muscle activity. Thus, each of pod structures 601, 602, 603, 604, 605, 606, and 607 may be referred to as a respective “sensor pod.” Throughout this specification and the appended claims, the term “sensor pod” is used to denote an individual pod structure that includes at least one sensor responsive to (i.e., to detect and provide at least one signal in response to) muscle activity of a user.

Pod structure 608 of device 600 includes a processor 630 that processes the signals provided by the capacitive EMG sensors 610 of sensor pods 601, 602, 603, 604, 605, 606, and 607 in response to detected muscle activity. Pod structure 608 may therefore be referred to as a “processor pod.” Throughout this specification and the appended claims, the term “processor pod” is used to denote an individual pod structure that includes at least one processor to process signals. The processor may be any type of processor, including but not limited to: a digital microprocessor or microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), a graphics processing unit (GPU), a programmable gate array (PGA), a programmable logic unit (PLU), or the like, that analyzes or otherwise processes the signals to determine at least one output, action, or function based on the signals. A person of skill in the art will appreciate that implementations that employ a digital processor (e.g., a digital microprocessor or microcontroller, a DSP, etc.) may advantageously include a non-transitory processor-readable storage medium or memory communicatively coupled thereto and storing data and/or processor-executable instructions that control the operations thereof, whereas implementations that employ an ASIC, FPGA, or analog processor may or may optionally not include a non-transitory processor-readable storage medium, or may include on-board registers or other non-transitory storage structures.

As used throughout this specification and the appended claims, the terms “sensor pod” and “processor pod” are not necessarily exclusive. A single pod structure may satisfy the definitions of both a “sensor pod” and a “processor pod” and may be referred to as either type of pod structure. For greater clarity, the term “sensor pod” is used to refer to any pod structure that includes a sensor and performs at least the function(s) of a sensor pod, and the term processor pod is used to refer to any pod structure that includes a processor and performs at least the function(s) of a processor pod. In device 600, processor pod 608 includes a capacitive EMG sensor 610 (not visible in FIG. 6 ) adapted to, in use, resistively couple to the user's skin in order to sense, measure, transduce or otherwise detect muscle activity of the user, so processor pod 608 could be referred to as a sensor pod. However, in exemplary device 600, processor pod 608 is the only pod structure that includes a processor 630, thus processor pod 608 is the only pod structure in exemplary device 600 that can be referred to as a processor pod. The processor 630 in processor pod 608 also processes the EMG signals provided by the capacitive EMG sensor 610 of processor pod 608. In alternative embodiments of device 600, multiple pod structures may include processors, and thus multiple pod structures may serve as processor pods. Similarly, some pod structures may not include sensors, and/or some sensors and/or processors may be laid out in other configurations that do not involve pod structures.

In device 600, processor 630 includes and/or is communicatively coupled to a non-transitory processor-readable storage medium or memory 640. Memory 640 may store processor-executable gesture identification instructions that, when executed by processor 630, cause processor 630 to process the EMG signals from capacitive EMG sensors 610 and identify a gesture to which the EMG signals correspond. For communicating with a separate electronic device (not shown), wearable EMG device 600 includes at least one communication terminal. Throughout this specification and the appended claims, the term “communication terminal” is generally used to refer to any physical structure that provides a telecommunications link through which a data signal may enter and/or leave a device. A communication terminal represents the end (or “terminus”) of communicative signal transfer within a device and the beginning of communicative signal transfer to/from an external device (or external devices). As examples, device 600 includes a first communication terminal 651 and a second communication terminal 652. First communication terminal 651 includes a wireless transmitter (i.e., a wireless communication terminal) and second communication terminal 652 includes a tethered connector port 652. Wireless transmitter 651 may include, for example, a Bluetooth® transmitter (or similar) and connector port 652 may include a Universal Serial Bus port, a mini-Universal Serial Bus port, a micro-Universal Serial Bus port, a SMA port, a THUNDERBOLT® port, or the like.

For some applications, device 600 may also include at least one inertial sensor 660 (e.g., an inertial measurement unit, or “IMU,” that includes at least one accelerometer and/or at least one gyroscope) responsive to (i.e., to detect, sense, or measure and provide at least one signal in response to detecting, sensing, or measuring) motion effected by a user. Signals provided by inertial sensor 660 may be combined or otherwise processed in conjunction with signals provided by capacitive EMG sensors 610.

As previously described, each of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 may include circuitry (i.e., electrical and/or electronic circuitry). FIG. 6 depicts circuitry 611 inside the inner volume of sensor pod 601, circuitry 612 inside the inner volume of sensor pod 602, and circuitry 618 inside the inner volume of processor pod 618. The circuitry in any or all of pod structures 601, 602, 603, 604, 605, 606, 607 and 608 (including circuitries 611, 612, and 618) may include any or all of: an amplification circuit to amplify electrical signals provided by at least one EMG sensor 610, a filtering circuit to remove unwanted signal frequencies from the signals provided by at least one EMG sensor 610, and/or an analog-to-digital conversion circuit to convert analog signals into digital signals. The circuitry in any or all of pod structures 601, 602, 603, 604, 605, 606, 607, and 608 may include one or more discrete component capacitor(s), resistor(s), and/or amplifier(s) in the configuration(s) previously described for sensors 200, 300, and/or 400. Device 600 may also include at least one battery (not shown in FIG. 6 ) to provide a portable power source for device 600.

Each of EMG sensors 610 includes a respective capacitive EMG sensor responsive to muscle activity corresponding to a gesture performed by the user, wherein in response to muscle activity corresponding to a gesture performed by the user each of EMG sensors 610 provides signals. EMG sensors 610 are capacitive EMG sensors that are adapted to, in use, resistively couple to the user's skin per the present systems, articles, and methods, as described for sensor 200 from FIG. 2 , sensor 300 from FIG. 3 , or sensor 400 from FIG. 4 . In particular, each EMG sensor 610 includes a respective first resistive sensor electrode 671 (only one called out to reduce clutter) that is communicatively coupled to an amplifier (not visible in FIG. 6 , but similar to amplifier 250 of sensor 200) through a discrete component capacitor (not visible in FIG. 6 , but akin to first capacitor 221 a of sensor 200) and a discrete component resistor (also not visible in FIG. 6 , but akin to first resistor 231 a of sensor 200), a second resistive sensor electrode 672 (only one called out to reduce clutter) that is also communicatively coupled to the amplifier through a discrete component capacitor (not visible in FIG. 6 , but akin to third capacitor 221 b of sensor 200) and a discrete component resistor (also not visible in FIG. 6 , but akin to third resistor 231 b of sensor 200), and a ground electrode 673 (only one called out to reduce clutter). Each of the electrodes 671, 672, and 673 of each EMG sensor 610 may be carried by a respective substrate, and the respective circuitry (e.g., 611, 612, and 618) of each pod structure 601, 602, 603, 604, 605, 606, 607, and 608 may be carried by the same substrate and include the communicative pathway, amplifier, capacitor, and resistor elements previously described for sensors 200, 300, and 400. For example, each respective EMG sensor 610 of each pod structure 601, 602, 603, 604, 605, 606, 607, and 608 may include a respective substrate, with the first and second sensor electrodes 671, 672 and the ground electrode 673 of each pod structure 601, 602, 603, 604, 605, 606, 607, and 608 carried by a first surface of the substrate and circuitry 611, 612, 618 carried by a second surface of the substrate, the second surface being opposite the first surface across a thickness of the substrate. For each sensor 610, the circuitry respectively includes at least an amplifier (e.g., 250, 350, 450), a first electrically conductive pathway (e.g., 211 a, 311 a, 411 a) that communicatively couples the first sensor electrode 671 and the amplifier, a first capacitor (e.g., 221 a, 321 a, 421 a) electrically coupled in series between the first sensor electrode 671 and the amplifier in the first electrically conductive pathway, and a first resistor (e.g., 231 a, 331 a, 431 a) electrically coupled in series between the first sensor electrode and the amplifier in the first electrically conductive pathway.

The capacitive EMG sensors 610 of wearable EMG device 600 are differential sensors that each implement two respective sensor electrodes 671, 672 and a respective ground electrode 673, though the teachings herein may similarly be applied to wearable EMG devices that employ single-ended capacitive EMG sensors that each implement a respective single sensor electrode and/or capacitive EMG sensors that share a common ground electrode.

Signals that are provided by capacitive EMG sensors 610 in device 600 are routed to processor pod 608 for processing by processor 630. To this end, device 600 employs a set of communicative pathways (e.g., 621 and 622) to route the signals that are output by sensor pods 601, 602, 603, 604, 605, 606, and 607 to processor pod 608. Each respective pod structure 601, 602, 603, 604, 605, 606, 607, and 608 in device 600 is communicatively coupled to, over, or through at least one of the two other pod structures between which the respective pod structure is positioned by at least one respective communicative pathway from the set of communicative pathways. Each communicative pathway (e.g., 621 and 622) may be realized in any communicative form, including but not limited to: electrically conductive wires or cables, ribbon cables, fiber-optic cables, optical/photonic waveguides, electrically conductive traces carried by a rigid printed circuit board, electrically conductive traces carried by a flexible printed circuit board, and/or electrically conductive traces carried by a stretchable printed circuit board.

Device 600 from FIG. 6 represents an example of a wearable EMG device that incorporates the teachings of the present systems, articles, and methods, though the teachings of the present systems, articles, and methods may be applicable to any wearable EMG device that includes at least one EMG sensor.

Throughout this specification and the appended claims, infinitive verb forms are often used. Examples include, without limitation: “to detect,” “to provide,” “to transmit,” “to communicate,” “to process,” “to route,” and the like. Unless the specific context requires otherwise, such infinitive verb forms are used in an open, inclusive sense, that is as “to, at least, detect,” to, at least, provide,” “to, at least, transmit,” and so on.

The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein of the various embodiments can be applied to other portable and/or wearable electronic devices, not necessarily the exemplary wearable electronic devices generally described above.

In the context of this disclosure, a memory is a processor-readable medium that is an electronic, magnetic, optical, or other physical device or means that contains or stores a computer and/or processor program. Logic and/or the information can be embodied in any processor-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions associated with logic and/or information.

In the context of this specification, a “non-transitory processor-readable medium” can be any element that can store the program associated with logic and/or information for use by or in connection with the instruction execution system, apparatus, and/or device. The processor-readable medium can be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, provided that it is tangible and/or non-transitory. More specific examples (a non-exhaustive list) of the processor-readable medium would include the following: a portable computer diskette (magnetic, compact flash card, secure digital, or the like), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory), a portable compact disc read-only memory (CDROM), digital tape, and other non-transitory media.

The various embodiments described above can be combined to provide further embodiments. To the extent that they are not inconsistent with the specific teachings and definitions herein, all of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to U.S. Non-Provisional patent application Ser. No. 14/553,657; U.S. Provisional Patent Application Ser. No. 61/909,786; U.S. Provisional Patent Application Ser. No. 61/768,322 (now U.S. Non-Provisional patent application Ser. No. 14/186,889); U.S. Provisional Patent Application Ser. No. 61/771,500 (now U.S. Non-Provisional patent application Ser. No. 14/194,252); U.S. Provisional Patent Application Ser. No. 61/857,105 (now U.S. Non-Provisional patent application Ser. No. 14/335,668); U.S. Provisional Patent Application Ser. No. 61/860,063 (now U.S. Non-Provisional patent application Ser. No. 14/276,575); U.S. Provisional Patent Application Ser. No. 61/866,960 (now U.S. Non-Provisional patent application Ser. No. 14/461,044); U.S. Provisional Patent Application Ser. No. 61/869,526 (now U.S. Non-Provisional patent application Ser. No. 14/465,194); U.S. Provisional Patent Application Ser. No. 61/881,064 (now U.S. Non-Provisional patent application Ser. No. 14/494,274); U.S. Provisional Patent Application Ser. No. 61/894,263 (now U.S. Non-Provisional patent application Ser. No. 14/520,081), and U.S. Provisional Patent Application Ser. No. 61/903,238 (now U.S. Non-Provisional patent application Ser. No. 14/539,773), are all incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

What is claimed is:
 1. A method comprising: at a wearable device that includes a sensor electrode and a circuit associated with the sensor electrode for processing muscular activity signals from a wearer of the wearable device: receiving, via the sensor electrode and while the circuit is tuned to operate using a first impedance, a first muscular activity signal; in response to detecting a variation in impedance at an interface between the sensor electrode and a skin portion of the wearer, electrically tuning the circuit to operate using a second impedance, distinct from the first impedance; and receiving, via the sensor electrode and while the circuit is tuned to operate using the second impedance, a second muscular activity signal.
 2. The method of claim 1, wherein the wearable device further includes an electrically conductive pathway that communicatively couples the sensor electrode and the circuit through a first capacitor and a first resistor.
 3. The method of claim 2, wherein the first sensor electrode is configured to resistively couple to the skin portion of the wearer.
 4. The method of claim 3, wherein the first capacitor comprises a discrete component capacitor configured to provide a fixed capacitance.
 5. The method of claim 4, wherein the circuit is tuned to the fixed capacitance provided by the discrete component capacitor.
 6. The method of claim 2, wherein the first capacitor is configured to galvanically isolate the circuit from the skin portion of the wearer.
 7. The method of claim 6, where the first resistor is configured to dominate impedance of the resistive coupling between the first sensor electrode and the skin portion of the wearer.
 8. The method of claim 2, wherein the circuit includes at least a portion of a circuit selected from the group consisting of: an amplification circuit, a filtering circuit, or an analog-to-digital conversion circuit.
 9. The method of claim 2, wherein the wearable device further comprises a ground electrode to resistively couple to another skin portion of the wearer, wherein the ground electrode includes a plate of electrically conductive material, and wherein the ground electrode is communicatively coupled to the circuit.
 10. The method of claim 2, wherein the wearable device further includes: a second sensor electrode configured to resistively couple to a second skin portion of the user; a second capacitor configured to galvanically isolate the circuit from the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit; and a second resistor configured to dominate impedance of the resistive coupling between the second sensor electrode and the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit.
 11. The method of claim 10, wherein the circuit comprises a high-pass filter that includes the first capacitor and the second resistor.
 12. The method of claim 11, wherein the circuit comprises a low-pass filter that includes the first resistor and the second capacitor.
 13. A wearable device comprising: a sensor electrode configured to receive muscular activity signals from a wearer of the wearable device; a circuit associated with the sensor electrode, and tuned to operate using a first impedance, configured to process muscular activity signals from a wearer of the wearable device; and a tuning component configured to electrically tune the circuit to operate using a second impedance, distinct from a first impedance in response to detecting a variation in impedance at an interface between the electrode and a skin portion of the wearer.
 14. The wearable device of claim 13, further comprising an electrically conductive pathway that communicatively couples the sensor electrode and the circuit through a first capacitor and a first resistor.
 15. The wearable device of claim 14, further comprising: a second sensor electrode configured to resistively couple to a second skin portion of the wearer; a second capacitor configured to galvanically isolate the circuit from the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit; and a second resistor configured to dominate impedance of the resistive coupling between the second sensor electrode and the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit.
 16. The wearable device of claim 14, wherein the first resistor has a magnitude of at least 1 kΩ.
 17. The wearable device of claim 13, wherein the sensor electrode has a first layer of a first electrically conductive material, and the first layer of the first electrically conductive material comprises copper.
 18. The wearable device of claim 17, wherein the sensor electrode includes: a second layer of a second electrically conductive material that includes a material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, or electrically conductive silicone.
 19. The wearable device of claim 18, further comprising: a housing, wherein the circuit, the first capacitor, and the first layer of the sensor electrode are all substantially contained within the housing, the housing including a hole, and wherein at least a portion of the second layer of the sensor electrode extends out of the housing through the hole.
 20. A wearable electromyography (“EMG”) device, comprising: an EMG sensor electrode configured to receive muscular activity signals from a wearer of the wearable device; a circuit associated with the EMG sensor electrode, and tuned to operate using a first impedance, configured to process muscular activity signals from a wearer of the wearable device; and a tuning component configured to electrically tune the circuit to operate using a second impedance, distinct from a first impedance in response to detecting a variation in impedance at an interface between the electrode and a skin portion of the wearer.
 21. The method of claim 1, wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least one portion of their hand, and the hand gestures, when detected, are configured to control a user interface on the wearable device or a head-wearable device.
 22. The wearable device of claim 13, wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least one portion of their hand, and the hand gestures, when detected, are configured to control a user interface on the wearable device or a head-wearable device.
 23. The wearable EMG device of claim 20, wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least of one portion their hand, and the hand gestures, when detected, are configured to control a user interface on the wearable EMG device or a head-wearable device. 